CVE-2026-68431

ksmbd: validate minimum PDU size for transform requests

State: Published
Severity: 9.1 Critical
Published: Aug 12, 2026
Updated: Aug 23, 2026
Reserved: Jul 30, 2026

Description

In the Linux kernel, the following vulnerability has been resolved:

ksmbd: validate minimum PDU size for transform requests

The receive path applies the minimum SMB2 PDU size check only when ProtocolId is SMB2_PROTO_NUMBER. A packet carrying SMB2_TRANSFORM_PROTO_NUM bypasses the check even when the negotiated dialect does not provide transform handling.

On an SMB 2.1 connection, a short transform packet therefore reaches init_smb2_rsp_hdr(), which interprets the request as a full SMB2 header and reads beyond the request allocation. The copied fields can then be returned to the unauthenticated client.

Compression transforms are converted to ordinary SMB2 messages before protocol validation. After that conversion, validate ordinary SMB2 requests against SMB2_MIN_SUPPORTED_PDU_SIZE and require encryption transform requests to contain both a transform header and an SMB2 header. This rejects truncated requests before work allocation.

Scores

CVSS	Score	Vector	Source
3.1	9.1 Critical	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H	Linux

Weaknesses

The record names no weakness.

Affected Products

Product	Versions
LinuxLinux	df3a4518aee64f21bcafa891105b468413f27431 to before 22f1aa35b87e471cc31b35b74451f46630863b12Affected 543c12c2644e772caa6880662c2a852cfdc5a10c to before 928dda88d0e13fbca381255028f65b244343a4eaAffected 368ba06881c395f1c9a7ba22203cf8d78b4addc0 to before d8e5c5672724b8f3c4c099d2cf60239c996e5424Affected 368ba06881c395f1c9a7ba22203cf8d78b4addc0 to before 32e486b70c256d5ef4baa5a2936ade2fea50e8ebAffected 368ba06881c395f1c9a7ba22203cf8d78b4addc0 to before d9e9753dfd43bd27c956578df7804a3c90b80fdcAffected 368ba06881c395f1c9a7ba22203cf8d78b4addc0 to before b62c510f59803f82f9b4c76ead2a56833b2984c7Affected 368ba06881c395f1c9a7ba22203cf8d78b4addc0 to before cfc0b8e5080aec87700774e8568765eaa4b7b92bAffected e9cb7be2fcbaee9e808b729e92948d38d52e5addAffected 5.15.145 to before 5.15.217Affected 6.1.34 to before 6.1.184Affected 6.3.8 to before 6.4Affected
LinuxLinux	6.4Affected before 6.4Not affected 5.15.217 through 5.15.Not affected 6.1.184 through 6.1.Not affected 6.6.153 through 6.6.Not affected 6.12.105 through 6.12.Not affected 6.18.46 through 6.18.Not affected 7.1.6 through 7.1.Not affected 7.2 and laterNot affected

Product

Versions

LinuxLinux

df3a4518aee64f21bcafa891105b468413f27431 to before 22f1aa35b87e471cc31b35b74451f46630863b12Affected
543c12c2644e772caa6880662c2a852cfdc5a10c to before 928dda88d0e13fbca381255028f65b244343a4eaAffected
368ba06881c395f1c9a7ba22203cf8d78b4addc0 to before d8e5c5672724b8f3c4c099d2cf60239c996e5424Affected
368ba06881c395f1c9a7ba22203cf8d78b4addc0 to before 32e486b70c256d5ef4baa5a2936ade2fea50e8ebAffected
368ba06881c395f1c9a7ba22203cf8d78b4addc0 to before d9e9753dfd43bd27c956578df7804a3c90b80fdcAffected
368ba06881c395f1c9a7ba22203cf8d78b4addc0 to before b62c510f59803f82f9b4c76ead2a56833b2984c7Affected
368ba06881c395f1c9a7ba22203cf8d78b4addc0 to before cfc0b8e5080aec87700774e8568765eaa4b7b92bAffected
e9cb7be2fcbaee9e808b729e92948d38d52e5addAffected
5.15.145 to before 5.15.217Affected
6.1.34 to before 6.1.184Affected
6.3.8 to before 6.4Affected

LinuxLinux

6.4Affected
before 6.4Not affected
5.15.217 through 5.15.*Not affected
6.1.184 through 6.1.*Not affected
6.6.153 through 6.6.*Not affected
6.12.105 through 6.12.*Not affected
6.18.46 through 6.18.*Not affected
7.1.6 through 7.1.*Not affected
7.2 and laterNot affected

References

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